Kaolin clay is used in many industrial applications including pulp and paper and ceramics. In the paper industry, kaolin may be used to fill and coat fine paper. Filler grade kaolin of minus 2 micron size is required to have a brightness of 80 to 84 on the General Electric Brightness Standard used in the paper industry. Coating grade kaolin must have a higher brightness in a range of 83 to 89.
In the Wood Mountain and Willows formations in Southern Saskatchewan, there are extensive deposits of kaolinized sands in which quartz, feldspar and other impurities are present. These impurities contaminate the kaolin and lower its brightness level.
While there are many patents relating to the upgrading of kaolin to a high brightness level (which commands a significant premium in the market place), the prior art generally relates to specific unit operations which are incremental improvements to common practice or other prior art. The prior art by being directed to individual operations does not therefore contain a combination of unit operations laid out in a unique manner to process a variety of kaolin reserves and in particular those containing significant amounts of fine silica, feldspar and other minerals which detrimentally affects optical properties and can be an abrasive factor for paper making machines.
For example, there are patents dealing with oxidative bleaching such as U.S. Pat. Nos. 4,618,374 3,353,668, 3,655,038, Canadian Patent 1,090,833. Impurities leaching is dealt with in Canadian Patent 852,775; magnetic separation in Canadian Patent 991,609, Canadian Patent 1,023,770, U.S. Pat. Nos. 3,471,011, 4,419,228, 3,371,988; and a range of flocculation approaches is discussed in Canadian Patent 991,658, Canadian Patent 982,161, Canadian Patent 868,957, U.S. Pat. Nos. 3,850,653, 3,837,482, 3,737,333, and 3,725,100. Floatation techniques are disclosed, for example, in U.S. Pat. Nos. 4,629,556, 3,224,582, 3,861,934, 4,098,688, 4,518,491, 4,472,271 or Canadian Patent 1,045,642.
Conventional unit operations, or obvious combinations of technology such as noted above, are apparently unable to deal with the deposits of kaolin found in Saskatchewan which are known to contain substantial amounts of silica, feldspar, titanoferrometallics, metallic minerals and organics since no commercial plant exist despite the good freight and logical market such an operation would have. Most of the prior art deals with kaolin deposits such as those found in Georgia which have run of mine brightness levels in the 75-80 range whereas deposits such as those found in Saskatchewan have significantly lower brightness level in the range of 60 to 70. Therefore, the Saskatchewan deposits therefore present significant problems in upgrading the kaolin to filler and coating grade specifications.
Kaolinized sand deposits such as those found in Southern Saskatchewan contain a wide range of impurities that have prevented the commercialization of these deposits because the impurities have a detrimental effect on the chemical and physical properties of the kaolin. In addition to quartz and various silicates, there are a variety of metal based minerals in the deposit which effect the behaviour of the kaolin. These minerals are based on metals such as iron, titanium, zirconium, copper, zinc, calcium, and potassium and sodium with others dependent upon the location in the deposit. In "Economic Minerals of Saskatchewan" Special Publication #8 of the Saskatchewan Geological Society, Master reports that the deposit contains quartz, muscovite, oligoclase and various feldspars in conjunction with the kaolin. Hudson, in the same report indicates that coarse and fine kaolin contain iron, titanium, calcium, magnesium, sodium and potassium. In addition, the deposit contains organic matter which can range as high as 0.05%. It will be recognized by those skilled in the art that even small amounts of some of these impurities can make upgrading of the kaolin deposit to the lower brightness filler grade challenging and make the production of high brightness coating grades of kaolin very difficult.